1. Field of the Invention
The present invention relates to extraction or removal of elongated wire or rod-like elements from surrounding sheaths or conduits in which they have become stuck or lodged. The invention has particular application to the removal of thermocouples from their conduits in nuclear reactor vessels.
2. Description of the Prior Art
In monitoring the power distribution of the reactor core of a nuclear reactor, various instrumentation is used. One type of instrumentation is incore instrumentation, which includes fuel assembly outlet thermocouples. The thermocouples are located above the upper core plate at preselected fuel assembly locations. Each thermocouple is approximately 6 to 9 meters in length and about 3 to 4 mm in diameter, sheathed in stainless steel. Each thermocouple is disposed in a conduit 13, such thermocouple conduits being disposed in a thermocouple column in the upper internals of the reactor. In a four-loop reactor, there are five such thermocouple columns, for a total of 65 thermocouples.
During reactor refueling, the thermocouple electrical terminals must be disconnected from each of the thermocouples in order to permit removal of the reactor head. During this operation, it is common for an instrument column or one or more of the thermocouples therein to be damaged. In that event, the thermocouples must be removed from their conduits in the damaged column, or individual damaged thermocouples must be removed. This is accomplished by pulling the thermocouples upwardly.
However, frequently the thermocouples become stuck or lodged in their conduits. This can occur as a result of corrosion, for example, and is particularly common in reactors which have been in use for an extended period of time. In the event of a stuck thermocouple, the removal pulling force must be increased until, ultimately, if the thermocouple is not freed, it eventually stretches and breaks.
Attempts have been made to facilitate removal of stuck thermocouples without breaking them. One such technique involves the flowing of warm water down the thermocouple conduit for a long period of time (up to 10 or 12 hours per thermocouple, for example), in an attempt to loosen the thermocouple. But this process is very time consuming and requires separate attachment means and auxiliary heaters and the like. Furthermore, it requires considerable man-rem exposure.